The purpose of this project is to study in a correlated manner, the effects of variations in membrane lipid fluidity and lipid composition on immunological processes such as patching and capping of ligand-receptors on the lymphocyte surface,and lectin-induced mitogenesis of lymphocytes. Cells will be exposed to saturated and unsaturated fatty acid dispersions, and the incorporation of these into plasmalemmal phospholipids will be established and quantified. The microviscosities of the cell surface membranes will be analyzed by fluorescence polarization analysis. Similar experiments will be done with cholesterol depletion and enhancement in the surface membranes. The effects of these modulations of cell surface lipid structure and microviscosity will be related to changes in the kinetics of patching and capping, and lectin-induced mitogenesis. The mechanisms underlying such changes will be investigated in relations to changes in calcium permeability, the function and structure of the cytoskeleton, and membrane structure, in terms of phase-separations as detected by temperature shifts and freeze-cleave.